People who had previously had a mild or asymptomatic infection had significantly improved protection against the Kent and South African variants after a single dose of the mRNA vaccine.

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A single dose of COVID-19 vaccine strengthens protection against variants of the SARS-CoV-2 coronavirus, but only in those previously infected with the disease, according to a study.

The researchers looked at the UK and South African variants, but believe it is possible that the results apply to other circulating variants, such as the Brazil variants (P.1 ) and India (B.1.617 and B.1.618). .

The results, published in the journal Science, show that in those who have not been infected previously and who have so far received only a single dose of the vaccine, the immune response to the coronavirus variants of concern may be insufficient.

Researchers at Imperial College London, Queen Mary University London and University College London examined the immune responses of British health workers at Barts and Royal Free hospitals after their first dose of Pfizer vaccine / BioNTech.

They found that people who had previously had a mild or asymptomatic infection had significantly improved protection against the Kent and South African variants after a single dose of the mRNA vaccine. In those without previous COVID-19, the immune response was weaker after a first dose, leaving them potentially at risk for variants.

“Our results show that people who received their first dose of the vaccine and who have never been infected with SARS-CoV-2 are not fully protected against the circulating variants of concern,” said Rosemary Boyton, professor of SARS-CoV-2. immunology and respiratory. Medicine at Imperial College London, which led the research. “This study highlights the importance of implementing second doses of the vaccine to protect the population.”

The researchers analyzed the blood samples for the presence and levels of immunity against the original strain of SARS-CoV-2, as well as variants from Kent (B.1.1.7) and South Africa (B .1.351) of concern.

In addition to antibodies, the researchers also focused on two types of white blood cells: B cells, which ‘remember’ the virus, and T cells, which help B cells remember and destroy them. cells infected with the coronavirus.

They found that after a first dose of vaccine, a previous infection was associated with an enhanced response of T cells, B cells, and neutralizing antibodies, which could provide effective protection against SARS-CoV-2, as well as against variants from Kent and South Africa.

However, in people without previous infection with SARS-CoV-2, a single dose of the vaccine resulted in lower levels of neutralizing antibodies against SARS-CoV-2 and its variants, making them potentially vulnerable to infection. and stressing the importance of the second dose of vaccine. It is not clear what protection T cells provide.

Mutations in the Kent and South African variants resulted in T cell immunity that could be reduced, enhanced, or unchanged from the original strain, depending on genetic differences between people.

“Our data show that natural infection alone may not provide sufficient immunity against the variants,” Boyton said. “Increasing with a single dose of vaccine in people who have already had an infection probably does. As new variants continue to emerge, it is important to accelerate the global deployment of vaccines to reduce the transmission of the virus and eliminate the opportunities for new variations, ”she said.